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WO2021176037A1 - Procédé pour la séparation sélective de thorium et de cérium à partir d'un concentré solide comprenant ceux-ci et un ou plusieurs autres métaux des terres rares et solution acide de terres rares associée - Google Patents

Procédé pour la séparation sélective de thorium et de cérium à partir d'un concentré solide comprenant ceux-ci et un ou plusieurs autres métaux des terres rares et solution acide de terres rares associée Download PDF

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Publication number
WO2021176037A1
WO2021176037A1 PCT/EP2021/055557 EP2021055557W WO2021176037A1 WO 2021176037 A1 WO2021176037 A1 WO 2021176037A1 EP 2021055557 W EP2021055557 W EP 2021055557W WO 2021176037 A1 WO2021176037 A1 WO 2021176037A1
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WIPO (PCT)
Prior art keywords
weight
cerium
thorium
acid
composition
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Ceased
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PCT/EP2021/055557
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English (en)
Inventor
Tom R. JØRGENSEN
Fredrik RODAHL
Sigve Sporstøl
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Yara International ASA
REEtec AS
Original Assignee
Yara International ASA
REEtec AS
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Priority to BR112022016245A priority Critical patent/BR112022016245A2/pt
Priority to CN202180018052.XA priority patent/CN115210393B/zh
Priority to AU2021232626A priority patent/AU2021232626A1/en
Priority to EP21707886.4A priority patent/EP4114998A1/fr
Priority to CA3173594A priority patent/CA3173594A1/fr
Priority to US17/908,942 priority patent/US20230089345A1/en
Publication of WO2021176037A1 publication Critical patent/WO2021176037A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B59/00—Obtaining rare earth metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C22B3/065—Nitric acids or salts thereof
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/22—Treatment or purification of solutions, e.g. obtained by leaching by physical processes, e.g. by filtration, by magnetic means, or by thermal decomposition
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B60/00—Obtaining metals of atomic number 87 or higher, i.e. radioactive metals
    • C22B60/02—Obtaining thorium, uranium, or other actinides
    • C22B60/0291—Obtaining thorium, uranium, or other actinides obtaining thorium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to the field of rare earth metals and, more specifically, to the selec tive separation of thorium and cerium from a solid concentrate comprising compounds of tho rium, cerium and other rare earth metals.
  • the group of rare earth elements consists of seventeen chemical elements (cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scan- dium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y)).
  • the rare earth elements are all metals, and the group is often referred to as the "rare earths” or “rare earth metals”. These metals have many similar properties, which often causes them to be found together in geological deposits. When a rare earth metal is incorporated into a compound, it is referred to as a "rare earth compound”. Rare earths are also referred to as "rare earth oxides" because many of them are typically commercialized as oxide compounds.
  • Rare earth metals and alloys that contain them are used in many devices that people use every day such as computer memories, DVDs, rechargeable batteries, cellular phones, catalytic converters, magnets, fluorescent lighting, and much more.
  • Rare earths are used as catalysts, phosphors, and polishing compounds, where they are used for air pollution control, illuminated screens on electronic devices, and the polishing of optical-quality glass. All of these products are expected to experience a steep rising demand.
  • cerium has been found to interfere with the recovery of other rare earths. Therefore, in order to maximize the recovery of the rare earths other than cerium, the separation of cerium is necessary.
  • radioactive thorium is also often extracted along with rare earths metals.
  • radioactivity issues with thorium Zhu Z. et.al., "Separation of uranium and thorium from rare earths for rare earth production - A review", 2015, Minerals Engineering, Volume 77, p. 185-196
  • thorium should be removed as effectively as possible in order for a concentrate of rare earths to be handled safely.
  • radioactive thorium should effectively be separated from the rare earths for the concen trate of rare earths to be handled safely, for example in further purification steps;
  • cerium should also be effectively separated from the other rare earths in order to maxim ize the recovery of the rare earths other than cerium;
  • nitrophosphate process also known as the Odda process
  • the process involves acidifying phosphate rock with nitric acid to produce a mixture of phosphoric acid and calcium nitrate.
  • a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals, obtainable by neutralizing to pH 1.8 an aque ous composition comprising from 6 to 21 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, and amounts of compounds of thorium, cerium and one or more further rare earth metals, the weight% being relative to the total weight of the aqueous composition.
  • RU2573905C discloses a method that can be applied for processing and deactivating a rare-earth concentrate (REC) which is extracted from apatite concentrate and for processing the products of the processing of the REC such as phosphogypsum and phosphoric acid.
  • REC rare-earth concentrate
  • the rare-earth concentrate containing uranium and tho rium compounds, is dissolved in nitric acid with heating and agitation, resulting in the dissolution of any sludge.
  • the solution then is diluted with water and cooled. After this, hydrogen peroxide is added, resulting in the reduction of from 98.0 to 99.5 % of cerium (+4) to cerium (+3).
  • thorium is separated by co-precipitation with barium sulphate, through the addition of sulphates and soluble barium compounds, and neutralisation of the nitric acid solution to pH from 2.5 to 3.9, at from 35 to 45°C, for from 1.0 to 1.5 hours.
  • the barium-thorium cake and the nitric acid solution are separated by filtration.
  • US3111375 discloses a process in which the triva- lent rare earths are first separated from the cerium and the thorium. In a second step, the ce rium is separated from the thorium. A mixture of the oxides of the rare earths and of thorium is obtained from an alkaline attack of monazite, and subsequent drying and heating in the pres ence of air to a temperature above 100 °C, preferably between 130 °C and 140 °C, thus trans forming the cerium contained in the mixture into ceric oxide.
  • US3594117 (Sylvania Electric Products Inc., 1971) relates to a process for removing cerium and thorium from other rare earths metals at a pH from about 4 to 5 and using iodate ions.
  • Hydrometallurgy 184 (2019) 140-150 (Queen's University, Springfield, Canada) relates to oxidative precipitation of cerium in acidic chloride solutions using hydrogen peroxide, sodium hypochlorite, potassium permanganate and Caro's Acid.
  • DD65075 (Albert Krause, Heinz Schade, Dr. Herfried Richter, 1969) relates to a method for obtaining rare earths contained in rock phosphates in the form of rare earth phosphates as a by product in the manufacture of certain multi-nutrient fertilizers, wherein a potassium perman ganate solution is used.
  • a method for separating thorium and cerium from a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals said solid concentrate obtainable by neutralizing to pH 1.8 the pH of an aqueous composition comprising from 6 to 21 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, and amounts of compounds of thorium, cerium and one or more further rare earth metals, the weight% being relative to the total weight of the aqueous composition, and subsequently precipitating and separating the solid concentrate comprising the compounds of thorium and cerium, comprising the steps of: a) contacting the solid concentrate with an acid such as to achieve a composition with a pH of less than 0.5; b) reacting the acid composition obtained in step a) with ozone or heating the acid composition obtained in step a) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1
  • cerium and thorium can be selectively and simultaneously separated from other rare earths present in a solid rare earth concentrate, obtainable by neutralizing to pH 1.8 an aqueous composition comprising from 6 to 21 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, the weight% being relative to the total weight of the aqueous composition, and amounts of compounds of thorium, cerium and one or more further rare earth metals.
  • a concentrate is obtainable in the nitrophosphate process to produce nitrogen fertilizers.
  • the method yields an acidic rare earths solution depleted in both radioactive thorium, hence safe to handle, and in cerium, which allows subsequent optimal separation of the rare earths in the acidic solution.
  • group of one or more further rare earth metals does not comprise cerium.
  • a method for separating thorium and cerium from a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals.
  • the method comprises the steps of neutralizing to pH 1.8 the pH of an aqueous composition comprising from 6 to 21 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, and amounts of compounds of thorium, cerium and one or more further rare earth metals, the weight% being relative to the total weight of the aqueous composition, and subsequently precipitating and separating the solid concentrate com prising the compounds of thorium and cerium.
  • the method further comprises the steps of: a) contacting the solid concentrate with an acid such as to achieve a composition with a pH of less than 0.5; b) reacting the acid composition obtained in step a) with ozone or heating the acid composition obtained in step a) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition to an oxidation state of +IV; c) increasing, to at most 2, such as between 1 and 2, the pH of the composition ob tained in step b), resulting in the precipitation of thorium and cerium compounds; and d) separating the precipitated thorium and cerium compounds from the composition obtained in step c) to obtain an aqueous acidic rare earth solution depleted in tho rium and cerium.
  • step a) consists of contacting the solid concentrate, with an acid such as to achieve a suspension with a pH of less than 0.5, with the aim of digesting the solid concentrate.
  • the method fur ther comprises the steps of: a') contacting with an acid the precipitated thorium and cerium compounds obtained in step d) such as to achieve a composition with a pH of less than 0.5; b') reacting the acid composition obtained in step a') with ozone or heating the acid composition obtained in step a') at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition to an oxidation state of +IV; c') increasing, to at most 2, such as between pH 1 and 2, the pH of the composition obtained in step b'), resulting in the precipitation of thorium and cerium com pounds; and d') separating the precipitated thorium and cerium compounds from the composition obtained in step c') to obtain an aqueous acidic rare earth solution depleted in tho rium and cerium.
  • the method fur ther comprises the steps of: b") reacting the acid solution obtained in step d) with ozone or heating the acid solution obtained in step d) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition to an oxidation state of +IV; c") increasing, to at most 2, such as between pH 1 and 2, the pH of the solution obtained in step b"), resulting in the precipitation of thorium and cerium com pounds; and d") separating the precipitated thorium and cerium compounds from the composition obtained in step c") to obtain an aqueous acidic rare earth solution depleted in thorium and cerium.
  • the acid used in steps a) and a') is from 90 to 98 weight% sulphuric acid (i.e. sulphuric acid with a concentration of from 90 to 98 weight% ), from 70 to 72 weight% perchloric acid (i.e. perchloric acid with a concentration of from 70 to 72 weight%) or from 55 to 65 weight% nitric acid (i.e. nitric acid with a concentration of from 55 to 65 weight%).
  • the acid used in steps a) and a') is from 55 to 65 weight% nitric acid.
  • steps b), b') and b" are performed by heating the acid compositions obtained in steps a) and a') or the acid solution obtained in step d) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours.
  • the oxidizing agent in steps b), b') and b") is ozone.
  • the pH in steps c), c') and c") is increased to a value ranging from 1.1 to 1.4.
  • the aqueous com position from which the solid concentrate is obtainable comprises from 0.001 to 0.01 weight% of thorium, from 0.1 to 0.3 weight% of cerium, and from 0.1 to 0.7 weight% of further rare earth metals, the weight% being relative to the weight of the aqueous composition.
  • the aqueous com position from which the solid concentrate is obtainable comprises from 7 to 8 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, from 0.001 to 0.002 weight% of thorium, from 0.15 to 0.25 weight% of cerium, and from 0.25 to 0.65 weight% of further rare earth metals, the weight% being relative to the weight of the aqueous composition.
  • the aqueous com position from which the solid concentrate is obtainable comprises from 6.5 to 8 weight% nitric acid, from 26 to 31 weight% phosphoric acid, from 3.5 to 4.5 weight% calcium, from 0.006 to 0.009 weight% of thorium, from 0.14 to 0.2 weight% of cerium and from 0.2 to 0.56 weight% of further rare earth metals, the weight% being relative to the weight of the aqueous composition
  • the aqueous composition from which the solid concentrate is obtainable comprises 3.5 ⁇ 0.5 weight% calcium, the weight% being relative to the total weight of the aqueous composition.
  • the method fur ther comprises the steps of: e) contacting the solid concentrate with water; and f) separating the water from the solid concentrate; wherein steps e) and f) are performed prior to steps a) and a').
  • the aqueous com position from which the solid concentrate is obtainable is obtained by the steps of: digesting an amount of phosphate rock in nitric acid at about 65 °C to obtain a di gest; followed by removing calcium nitrate from the digest.
  • the aqueous com position from which the solid concentrate is obtainable is obtained by: digesting an amount of phosphate rock in nitric acid at about 65 °C to obtain a di gest; followed by removing calcium nitrate from the digest; and steps c), c') and c") are performed using ammonia, preferably gaseous ammonia.
  • the thorium and cerium compounds precipitated in step d) are recycled to a liquor of the nitrophosphate process comprising from 18 to 21 weight% nitric acid, from 25 to 29 weight% phosphoric acid and from 4 to 5 weight% calcium, and neutralized to pH 5.8, the weight% being relative to the total weight of the liquor.
  • an aqueous acidic rare earth solution com prising from 1 to 5 weight% rare earths, from 17 to 35 weight% nitric acid, from 3 to 8 weight% phosphoric acid, from 0.5 to 2.5 weight% calcium, less than 5000 ppm by weight cerium, less than 100 ppm by weight thorium, and about 0.1 g/l manganese, is disclosed.
  • a composition enriched in cerium and thorium compounds comprising from 4 to 6 weight% calcium, from 4 to 7 weight% phosphorous, from 10 to 17 weight% cerium, from 5 to 10 weight% other rare earths and from 0.5 to 1 weight% thorium.
  • the pH values in this application are the values measured from a sample prepared by subsequently sampling a composition for which a pH value is to be deter mined, weighing the amount of sampled composition, adding to the sampled composition 13 grams of water per gram of sampled composition and mixing the added water and the sampled composition so as to make a homogenous sample.
  • thorium and cerium can be separated from a solid composition comprising thorium, cerium and further rare earth metals, particular in concen trated form, by a (partial) dissolution of the solid concentrate at pH of less than 0.5 and oxidation of the cerium ions to an oxidation state of +IV; followed by precipitation of thorium and cerium compounds by raising the pH to at most pH 2 and separating the precipitated thorium and ce rium compounds, thus obtaining a aqueous acidic rare earth solution depleted in thorium and cerium.
  • step c) can be increased to the final pH value in a single step or stepwise.
  • a precipitate then is collected in step d) following each pH increas ing step c), until the final pH is reached. All precipitates obtained in step d) can then be combined or be subject to further treatment individually.
  • the solid concentrate is obtainable, for example, from the nitrophosphate process.
  • the nitrophosphate process comprises six main steps.
  • a first step phosphate rock is digested in nitric acid yielding a digestion liquor at a temperature of 65°C.
  • a second step crystallization step
  • calcium nitrate tetrahydrate is crystallized out of the digestion liquor yield ing a crystal slurry.
  • the crystallized calcium nitrate is separated by a technique such as filtration or centrifugation, resulting in calcium nitrate tetrahydrate crys tals being separated from the liquid of the crystal slurry, referred to as the mother liquor.
  • a fourth step the mother liquor is neutralized using ammonia up to a pH of approximately 5.8.
  • a fifth step the neutralized mother liquor is particulated into the final product (e.g. for use as an NP-fertilizer).
  • Potassium salts can be added during the neutralization process or to the neutralized mother liquor.
  • an evaporation step is performed upfront the addition of potassium salts, in order to reach a water content sufficiently low to perform prilling.
  • the par ticles can be subsequently coated, for example with a coating agent suitable for reducing mois ture absorption and for, thereby, ensuring proper physical properties for the particles.
  • the solid concentrate obtained by precipitation from the mother liquor at pH 1.8 may comprise from 9 to 11 weight% elemental phosphate, from 4 to 5 weight% cal cium, from 5 to 8 weight% cerium thorium, 100 to 300 ppm cerium and from 10 to 16 weight% total rare earth metal compounds, the weight% being relative to the total weight of the solid concentrate.
  • hydrogen peroxide it is preferred to not use hydrogen peroxide as an oxidizing agent: under acidic conditions, hydrogen peroxide may act as reducing agent rather than an oxidizing agent. It is also not pre ferred to use potassium permanganate as an oxidizing agent.
  • the method of the disclosure enables to deplete the solid concentrate mentioned above in thorium such that the ratio of the weight percentage of thorium over the weight percentage of non-cerium rare earths in the aqueous composition, from which the solid concentrate is pre pared, is reduced by 94 to 99% in the acidic solution obtained in step d).
  • the ratio of the weight percentage of cerium over the weight percentage of non-cerium rare earths in the aqueous composition, from which the solid concentrate is prepared, is reduced by 91 to 96% in the acidic solution obtained in step d).
  • the inventors have found that, by performing the method of the present dis closure, it is possible to simultaneously precipitate thorium and cerium from a solution compris ing thorium, cerium and one or more further rare earth metals.
  • a rare earth solution is obtained that can be safely handled since it comprises safe levels of thorium.
  • the solution further comprises sufficiently low levels of cerium such that a rare earth concentrate is obtained from which the recovery of the other rare earths than cerium can be maximized.
  • a method for separating thorium and cerium from a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals.
  • the method comprises the steps of neutralizing to pH 1.8 the pH of an aqueous composition comprising from 6 to 21 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, and amounts of compounds of thorium, cerium and one or more further rare earth metals, the weight% being relative to the total weight of the aqueous composition, and subsequently precipitating and separating the solid concentrate com prising the compounds of thorium and cerium.
  • the method further comprises the steps of: a) contacting the solid concentrate with an acid such as to achieve a composition with a pH of less than 0.5; b) reacting the acid composition obtained in step a) with an oxidizing agent, in partic ular ozone, or heating the acid composition obtained in step a) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition obtained in step a) to an oxidation state of +IV; c) increasing, to at most 2, such as between 1 and 2, the pH of the composition ob tained in step b), resulting in the precipitation of thorium and cerium compounds; and d) separating the precipitated thorium and cerium compounds from the composition obtained in step c) to obtain an aqueous acidic rare earth solution depleted in tho rium and cerium.
  • hydrogen peroxide it is preferred to not use hydrogen peroxide as an oxidizing agent: under acidic conditions, hydrogen peroxide may act as reducing agent rather than an oxidizing agent. It is also not pre ferred to use potassium permanganate as an oxidizing agent.
  • step a) consists of contacting the solid concentrate, with an acid such as to achieve a suspension with a pH of less than 0.5, with the aim of digesting the solid concentrate.
  • the acid used in step a) is from 60 to 65 weight% nitric acid.
  • 1 ml of 55 weight% nitric acid is used per g of concentrate to be digested.
  • the digestion may be partial or full. In a particular embodiment, the digestion is performed partially and, consequently, some solids remain present, which results in the obtention of a suspension in step a).
  • the method further comprises the steps of: a') contacting with an acid the precipitated thorium and cerium compounds obtained in step d) such as to achieve a composition with a pH of less than 0.5; b') reacting the acid composition obtained in step a') with an oxidizing agent, in partic ular ozone, or heating the acid composition obtained in step a') at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition to an oxidation state of +IV; c') increasing, to at most 2, such as between 1 and 2, the pH of the composition ob tained in step b'), resulting in the precipitation of thorium and cerium compounds; and d') separating the precipitated thorium and cerium compounds from the composition obtained in step c') to obtain an aqueous acidic rare earth solution depleted in tho
  • step c' can be increased to the final pH value in a single step or stepwise.
  • a precipitate then is collected in step d') following each pH increas ing step c), until the final pH is reached.
  • all precipitates obtained in step d') are combined.
  • hydrogen peroxide it is preferred to not use hydrogen peroxide as an oxidizing agent: under acidic conditions, hydrogen peroxide may act as reducing agent rather than an oxidizing agent. It is also not pre ferred to use potassium permanganate as an oxidizing agent.
  • the amount of rare earth metals recovered is optimized by performing, starting with the precipitated thorium and cerium compounds obtained in step d), the series of steps a') to d').
  • the steps a'), b'), c') and d') respectively correspond to the steps a), b), c) and d) performed starting with the solid concentrate used in step a). Repeating the series of steps a') to d'), starting with the precipitated thorium and cerium compounds obtained in steps d'), will further increase the recovery of rare earth metals.
  • the method further comprises the steps of: b") reacting the acid solution obtained in step d) with on oxidizing agent, in particular ozone, or heating the acid solution obtained in step d) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours, thereby oxidizing the cerium ions in the acid composition obtained in step d) to an oxidation state of +IV; c") increasing, to at most 2, such as between 1 and 2, the pH of the solution obtained in step b"), resulting in the precipitation of thorium and cerium compounds; and d") separating the precipitated thorium and cerium compounds from the composition obtained in step c") to obtain an aqueous acidic rare earth solution depleted in thorium and cerium.
  • step c" can be increased to the final pH value in a single step or stepwise.
  • a precipitate then is collected in step d") following each pH in creasing step c), until the final pH is reached.
  • aAII precipitates obtained in step d") are then combined.
  • hydrogen peroxide it is preferred to not use hydrogen peroxide as an oxidizing agent: under acidic conditions, hydrogen peroxide may act as reducing agent rather than an oxidizing agent. It is also not pre ferred to use potassium permanganate as an oxidizing agent.
  • the series of steps b") to d") optimizes the amounts of precipitated thorium and cerium compounds, hence the extent to which the acidic solution obtained in step d) is free of cerium and thorium.
  • the optimization of the precipitation of those cerium and thorium compounds is achieved by performing, on the acid solution obtained in step d) the steps b") to d"), b") and d") or c") and d").
  • the steps b"), c") and d") respectively correspond to the steps b), c) and d) performed starting with the solid concentrate used in step a).
  • the steps a) and a') are performed using from 90 to 98 weight% sulphuric acid, from 70 to 72 weight% perchloric acid or from 55 to 65 weight% nitric acid.
  • Such acid solutions are sufficiently strong for digesting the solid concentrate.
  • such acid solutions have oxidizing potential that can at least partially assist in performing step b).
  • the acid used in steps a) and a') is from 60 to 65 weight% nitric acid.
  • acid solutions it is possible to recycle the precipitated and filtered thorium and cerium compounds, bearing traces of the nitric acid solution, to processes comprising nitric acid, such as the nitrophosphate process described above and from which the solid concentrate is obtainable.
  • the recycling of the precipitated tho rium and cerium compounds results in those elements being diluted to acceptable, safe limits.
  • steps b), b') and b" are preferably performed by heating the acid compositions obtained in step a) and a') or the acid solution obtained in step d) at a temperature ranging from 110 °C to 130 °C for a time period ranging from 1 to 3 hours.
  • oxidation of the cerium ions to an oxidation state of +IV takes place and the acid used for digestion of the solid concentrate can act as the oxidizing agent, without intro duction of an additional chemical as the oxidizing agent.
  • the ratio of the weight percentage of thorium over the weight percentage of non-cerium rare earths in the aqueous composition is reduced by 94 to 99% in the acidic solution obtained in step d), and that the ratio of the weight percentage of cerium over the weight percentage of non-cerium rare earths in the aqueous composition is reduced by 91 to 96% in the acidic solution obtained in step d).
  • the heating time can be further optimised according to the con tent of the aqueous composition such as from 1 hour to 6 hours, or from one 1 hour to 8 hours, or from 1 hour to 10 hours such as to optimise the amount of cerium that is oxidised.
  • the oxidizing agent in steps b), b') and b" is ozone. It is preferred to not use hydrogen peroxide as an oxidizing agent: under acidic conditions, hydrogen peroxide may act as reducing agent rather than an oxidizing agent. It is also not preferred to use potassium permanganate as an oxidizing agent. Furthermore, the use of ozone as the oxidizing agent enables an adjustment of the pH in step c) to about 1, hence at a lower value than when other oxidizing agents are used. The use of ozone therefore results in optimal selectivity in the precipitation of cerium and thorium compounds.
  • the yield of an element is the ratio of the amount of the element in the nitric acid solution obtained in step d), d') and d") over the amount of the element in the rare earth concentrate digested in step a) and a') respectively.
  • the pH in steps c), c') and c") is increased to a value ranging from 1.1 to 1.4.
  • the precipitation of the thorium and cerium compounds is increased, while the rare earth metal compounds other than cerium compounds preserve higher solubility in nitric acid than thorium and cerium com pounds, enabling the selective precipitation of cerium and thorium compounds in steps c), c') and c")
  • the method of the disclosure also results in iron and aluminium metal compounds being separated together with the thorium and cerium compounds. As a result, the weight and volume of the rare earth concentrate obtained following the precipitation and the separation of the precipitated elements are reduced. Therefore, the subsequent processing of the acid solution obtained in steps d), d') and d") is facilitated.
  • the separating in step d) is done by filtering.
  • the aqueous compo sition from which the solid concentrate is obtainable comprises from 0.001 to 0.01 weight% of thorium, from 0.1 to 0.3 weight% of cerium, and from 0.1 to 0.7 weight% further rare earth metals, the weight% being relative to the total weight of the aqueous composition.
  • further rare earth metals means one or more non-cerium rare earth metals.
  • the aqueous compo sition from which the solid concentrate is obtainable comprises from 0.001 to 0.009 weight% of thorium, the weight% being relative to the total weight of the aqueous composition.
  • the aqueous compo sition from which the solid concentrate is obtainable comprises from 7 to 8 weight% nitric acid, from 25 to 33 weight% phosphoric acid, from 3.5 to 5 weight% calcium, from 0.001 to 0.002 weight% of thorium, from 0.15 to 0.25 weight% of cerium, and from 0.25 to 0.65 weight% of further rare earth metals, the weight% being relative to the total weight of the aqueous compo sition.
  • This aqueous composition corresponds to a nitrophosphate mother liquor produced using Kola phosphate rock as a raw material (originating from deposits in the Kola Peninsula, Russia).
  • the aqueous compo sition from which the solid concentrate is obtainable comprises from 6.5 to 8 weight% nitric acid, from 26 to 31 weight% phosphoric acid, from 3.5 to 4.5 weight% calcium, from 0.006 to 0.009 weight% of thorium, from 0.14 to 0.2 weight% of cerium and from 0.2 to 0.56 weight% of further rare earth metals, the weight% being relative to the total weight of the aqueous compo sition.
  • This aqueous composition corresponds to a nitrophosphate mother liquor produced using the Palfos phosphate rock as a raw material (originating from deposits in South Africa - see e.g. Phosphate in South Africa, E.H. Roux et al., J.S. Afr. Inst. Min. Metall., Vol 89, no. 5, May 1989, pp. 129-139).
  • the aqueous compo sition from which the solid concentrate is obtainable comprises 3.5 ⁇ 0.5 weight% calcium, the weight% being relative to the total weight of the aqueous composition.
  • the precipitation of thorium and ce rium compounds will be maximized as the competing precipitation of calcium phosphates will be minimized.
  • the method further comprising the steps of: e) contacting the solid concentrate with water; and f) separating the water from the solid concentrate; wherein steps e) and f) are performed prior to steps a) and a').
  • steps e) and f) result in the removal of water-soluble impurities from the solid concentrate which results in an opti mal, selective precipitation of cerium and thorium compounds in steps c), c') and c").
  • the aqueous compo sition from which the solid concentrate is obtainable is obtained by the steps of: digesting an amount of phosphate rock in nitric acid at about 65 °C to obtain a di gest; followed by removing calcium nitrate from the digest.
  • the aqueous composition from which the solid concentrate is obtainable is a nitrophosphate mother liquor.
  • a mother liquor is partic ularly suitable for producing a solid concentrate, rich in rare earth metals when phosphate rock raw materials, rich in those rare earth metals, are used to produce the nitrophosphate mother liquor.
  • Igneous phosphate rocks comprising more than 0.4 weight% of rare earth metals are particularly suitable for producing a solid concentrate.
  • any agent suitable for increasing the pH or, in other words, any conventional chemical base such as, but non-limited to, sodium hydroxide, potassium hydroxide or ammonium hydrox ide can be used for increasing the pH in steps c), c') and c").
  • any conventional chemical base such as, but non-limited to, sodium hydroxide, potassium hydroxide or ammonium hydrox ide
  • the increase of the pH in steps c), c') and c" is performed using gaseous ammonia.
  • step c), c') and c" no chemical is intro pokerd in the process that is not compatible with the nitrophosphate process. As mentioned above, this is particularly suitable in view of recycling the precipitated thorium and cerium com pounds to the nitrophosphate process.
  • the use of ammonia provides the advantage of minimizing the amount of water used in the process and results in energy savings.
  • ammonia is used in steps c), c') and c" of the method of the disclosure which, as described above, results in the precipitation of phosphate compounds of thorium and cerium.
  • those phosphate compounds may then be returned to a mother liquor of the nitrophosphate, comprising from 18 to 21 weight% nitric acid, from 25 to 29 weight% phosphoric acid and from 4 to 5 weight% calcium, and neutralized to pH 5.8, the weight% being relative to the total weight of the mother liquor.
  • the cerium and thorium compounds separated in steps d), d') and d" may be subjected to chemical reduction in order for cerium to be reduced to an oxidation state of +111.
  • the thorium and cerium compounds separated in step d), and that will be part of the fertilizer particles produced by the nitrophosphate process will have solubility properties such that that the phosphate in those compounds will be accessible to plants or crops, upon distribution of the fertilizer on the soil and subsequent irrigation of this soil, from which the plants or crops are to be grown.
  • an aqueous acidic rare earth solution comprising from 1 to 5 weight% rare earths, from 17 to 35 weight% nitric acid, from 3 to 8 weight% phosphoric acid, from 0.5 to 2.5 weight% calcium, less than 5000 ppm by weight cerium, less than 100 ppm by weight thorium, between 0 and 0.1 g/l manganese.
  • the aqueous rare earth solution from 300 ppm to 4000 ppm by weight cerium, or from 300 ppm to 3000 ppm by weight cerium, or from 300 ppm to 1000 ppm by weight cerium.
  • the aqueous rare earth solution comprises from 0.1 ppm to 100 ppm by weight thorium, such as from 1 ppm by weight to 50 ppm by weight thorium, or from 0.8 ppm by weight to 10 ppm by weight thorium.
  • a composition enriched in cerium and thorium compounds comprising from 4 to 6 weight% calcium, from 4 to 7 weight% phosphorous, from 10 to 17 weight% cerium, from 5 to 10 weight% other rare earths and from 0.5 to 1 weight% thorium.
  • Stage 1 Preparation of a solid concentrate comprising compounds of thorium, cerium and one or more further rare earth metals.
  • a neutralized Kola mother liquor was prepared according to the nitrophosphate process by
  • the resulting neutralized Kola mother liquor was partly neutralized with ammonia to pH 1.8, measured after diluting a sample with water by a weight factor of 13. A temperature of about 120 °C (boiling) was reached during the neutralization. The so-called neutralized solution (at pH 1.8) was then held at boiling temperature for 3 hours to facilitate the precipitation of cerium and thorium compounds. The liquid fraction was further treated in the nitrophosphate process for neutralization to pH 5.8, measured after diluting a sample with water by a weight factor of 13.
  • the solid fraction was washed in water and separated again to produce a solid concentrate comprising from 9 to 11 weight% elemental phosphate, from 4 to 5 weight% calcium, from 5 to 8 weight% cerium thorium, 100 to 300 ppm cerium and from 10 to 16 weight% total rare earth metal compounds, the weight% being relative to the total weight of the solid concentrate.
  • Stage 2 Separation of cerium and thorium from the rare earths in the solid concentrate.
  • the rare earths concentrate was digested during a time period of one hour in 55 weight% nitric acid, at an initial concentration of 1 ml of acid per g of the rare earths concentrate and at a temperature of about 120 °C.
  • the digested liquor was then neutralized with water and ammonia to pH 1.2, measured after diluting a sample with water by a weight factor of 13. This resulted in the precipitation of the cerium ions in a +IV oxidation state and in the tetravalent thorium ions as phosphate complexes.
  • the solution was then separated from the precipitated solids by filtra tion.
  • the filtered liquid fraction comprised 80 weight% of the rare earths other than cerium and initially present in the rare earths concentrate, about 5 weight% of the cerium initially present in the rare earths concentrate, and no thorium.
  • the solid fraction comprised cerium and thorium phosphate compounds. This solid fraction then was reintroduced in the nitrophosphate process, in the mother liquor neutralized to pH 5.8.

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Abstract

La présente invention concerne un procédé pour la séparation de thorium et de cérium à partir d'un concentré solide comprenant des composés de thorium, de cérium et d'un ou plusieurs autres métaux des terres rares, pouvant être obtenu par augmentation au pH 1,8, le pH d'une composition aqueuse comprenant de 6 à 21 % en poids d'acide nitrique, de 25 à 33 % en poids d'acide phosphorique, de 3,5 à 5 % en poids de calcium et certaines quantités de thorium, de cérium et d'un ou plusieurs autres métaux des terres rares, le pourcentage en poids étant par rapport au poids total de la composition aqueuse, et par la suite la précipitation et la séparation du concentré solide comprenant les composés de thorium et de cérium. Le procédé comprend les étapes consistant à a) mettre en contact le concentré solide avec un acide de manière à obtenir une composition ayant un pH inférieur à 0,5, b) faire réagir la composition acide obtenue à l'étape a) avec de l'ozone ou chauffer la composition acide obtenue à l'étape a) à une température allant de 110 °C à 130 °C pendant une durée allant de 1 à 3 heures, ce qui permet d'oxyder les ions cérium présents dans la composition acide jusqu'à un état d'oxydation de + IV, c) augmenter, jusqu'à au maximum 2, par exemple entre 1 et 2, la valeur de pH de la composition obtenue à l'étape b), ce qui entraîne la précipitation de composés de thorium et de cérium, et d) séparer le concentré solide comprenant les composés de thorium et de cérium de la composition obtenue à l'étape c) pour obtenir une solution aqueuse acide de terres rares appauvrie en thorium et en cérium. La présente invention concerne en outre une solution aqueuse acide de terres rares appauvrie en thorium et en cérium, pouvant être obtenue par un procédé selon le procédé de l'invention.
PCT/EP2021/055557 2020-03-06 2021-03-05 Procédé pour la séparation sélective de thorium et de cérium à partir d'un concentré solide comprenant ceux-ci et un ou plusieurs autres métaux des terres rares et solution acide de terres rares associée Ceased WO2021176037A1 (fr)

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BR112022016245A BR112022016245A2 (pt) 2020-03-06 2021-03-05 Método para separação seletiva de tório e cério a partir de um concentrado sólido compreendendo o mesmo e um ou mais outros metais de terras raras e solução ácida de terras raras dos mesmos
CN202180018052.XA CN115210393B (zh) 2020-03-06 2021-03-05 从固体精矿中选择性分离钍和铈的方法
AU2021232626A AU2021232626A1 (en) 2020-03-06 2021-03-05 Method for selective separation of thorium and cerium from a solid concentrate comprising same and one or more further rare earth metals and acidic rare earth solution thereof
EP21707886.4A EP4114998A1 (fr) 2020-03-06 2021-03-05 Procédé pour la séparation sélective de thorium et de cérium à partir d'un concentré solide comprenant ceux-ci et un ou plusieurs autres métaux des terres rares et solution acide de terres rares associée
CA3173594A CA3173594A1 (fr) 2020-03-06 2021-03-05 Procede pour la separation selective de thorium et de cerium a partir d'un concentre solide comprenant ceux-ci et un ou plusieurs autres metaux des terres rares et solution acide de terres rares associee
US17/908,942 US20230089345A1 (en) 2020-03-06 2021-03-05 Method for selective separation of thorium and cerium from a solid concentrate comprising same and one or more further rare earth metals and acidic rare earth solution thereof

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EP20161399.9A EP3875618A1 (fr) 2020-03-06 2020-03-06 Procédé de séparation sélective de thorium et de cérium à partir d'un concentré solide le comprenant et un ou plusieurs métaux de terres rares et sa solution d'acide de terres rares

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WO2025048766A3 (fr) * 2022-07-26 2025-04-03 The Penn State Research Foundation Précipitation oxydative à l'ozone d'éléments à partir de flux aqueux
RU2818214C1 (ru) * 2023-03-01 2024-04-25 Федеральное государственное автономное образовательное учреждение высшего образования "Уральский федеральный университет имени первого Президента России Б.Н. Ельцина" Способ извлечения редкоземельных элементов из азотно-фосфорнокислого раствора при азотнокислотной переработке апатитового концентрата

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AU2021232626A1 (en) 2022-10-13
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